1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to an apparatus and method for allocating subcarriers in a mobile communication system.
2. Description of the Related Art
Most of factors that impede high-speed, high-quality data services arise from channel environment in a wireless mobile communication system. The channel environment often varies due to Additive White Gaussian Noise (AWGN), fading which causes changes in the power of a received signal, shadowing, the Doppler effect resulting from the movement and frequent velocity change of a Mobile Station (MS), interference from other MSs, and multi-path interference.
Thus, an advanced technology is required for providing high-speed wireless data packet service. Obviously, techniques adopted in legacy mobile communication systems, such as Adaptive Modulation and Coding (AMC) and Hybrid Automatic Repeat Request (HARQ) remarkably improved overall system performance by adapting to the variant channel environment.
However, these techniques are not effective in solving the problem of shortage of radio resources. That is, a multiple access scheme with excellent spectrum efficiency needs to be developed in order to maximize system capacity and enable high-speed data transmission critical to multimedia service. Accordingly, a novel multiple access scheme is required which offers excellent spectrum efficiency and ensures data priority, for high-speed, high-quality packet data service.
An Orthogonal Frequency Division Multiple Access (OFDMA) mobile communication system allocates frequency resources to MSs on a subcarrier basis. Thus, the OFDMA mobile communication system can increase data rate under a given channel condition by use of the appropriate adaptation technique.
Yet, the dynamic channel allocation and dynamic resource allocation schemes of a typical OFDMA mobile communication system are intended for a fixed wireless network based on the assumption that MSs are fixed at predetermined positions. In this case, each MS reports the Signal-to-Noise Ratios (SNRs) of all subcarriers to a BS and the BS allocates subcarriers, i.e. subcarrier channels and resources to the MS based on the SNRs. When one or more subcarriers are allocated to a particular MS, it is assumed that the channel status of the subcarriers is kept unchanged.
In the OFDMA mobile communication system, the MS has to frequently report its Channel State Information (CSI) because of the time-variant property of channels. As a consequence, a joint bit, subcarrier, and signal power allocation algorithm based on full knowledge of channel status for the OFDMA mobile communication system brings about excess signaling overhead on the uplink. Moreover, the signaling overhead makes it impossible to implement such a subcarrier allocation scheme in practice.
Accordingly, there exists a need for developing a subcarrier allocation scheme for improving system performance with an appropriate level of overhead.